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This study used PHITS and Geant4 code packages to simulate a Leksell Gamma Knife system in order to determine radiation dose distribution in two types of phantoms. The results observed in the water phantom with configurations of single source and 201 sources are in good accord with the prior research, including both simulation and experiment. Several characteristics of Leksell Gamma Knife 4C, such as dose profiles, output factor, FWHM, and penumbra size, are calculated based on Monte Carlo simulations, which show the best consistency with other results. The output factors for collimators of 14 mm, 8 mm, and 4 mm are 0.984, 0.949, and 0.872, respectively. The simulation results with an adult mesh-type reference phantom reveal considerable similarities with the established radiosurgery plans. It indicates that the absorbed dose in brain tumors was highest when utilizing the 18 mm collimator and subsequently reduced with collimator size to 0.65, 0.25, and 0.5 with the 14 mm, 8 mm, and 4 mm collimators, respectively. The absorbed dose has a very low value for other essential organs and decreases with distance from the brain tumor. These findings may explain why the dose to organs decreases linearly as target distance, volume, and collimator size increase.

In this paper, the fast neutron spectra at altitudes of 3 and 5 km were unfolded by the response of Superheated Drop Detectors and using an Adaptive Network-based Fuzzy Inference System (ANFIS). ANFIS is a Takagi-Sugeno Fuzzy Inference System implemented in the framework of adaptive networks. This tool works similarly to human thinking in dealing with uncertain and erroneous problems. The response matrix of five Superheated Drop Detectors under various external pressures was calculated by an application developed using the Geant4 simulation toolkit and was used to obtain inputs of ANFIS. Also, the neutron spectra of the IAEA technical reports were utilized as the targets. The reference spectra were unfolded with RMSEs of 0.005 and 0.011. The relative agreement between the unfolded and reference spectra shows that these detectors and ANFIS can be used as a new technique for unfolding neutron spectra produced by cosmic radiations in the atmosphere.

We investigated the influence of modifying the voltage of an X-ray tube with a tungsten anode between 30 kV and 225 kV, and therefore its photon energy spectrum (up to 225 keV), on the Total Ionizing Dose deposited in a single-mode, phosphorus-doped optical fiber, already identified as a promising dosimeter. Simulation data, obtained using a toolchain combining SpekPy and Geant4 software, are compared to experimental results obtained on this radiosensitive optical fiber and demonstrate an increase of the deposited dose with operating voltage, at a factor of 4.5 between 30 kV and 225 kV, while keeping the same operating current of 20 mA. Analysis of simulation results shows that dose deposition in such optical fibers is mainly caused by the low-energy part of the spectrum, with 90% of the deposited energy originating from photons with an energy below 30 keV. Comparison between simulation and various experimental measurements indicates that phosphosilicate fibers are adapted for performing X-ray dosimetry at different voltages.

Abstract X‐ray diffraction from a solid crystal shows the wave nature of photons. It is an important electromagnetic (EM) physics process when X‐ray photons interact with a crystal. Bragg diffraction, often called Bragg reflection, is a special case of the general form of X‐ray diffraction, known as Laue diffraction. When the Bragg's law is met, the incident photon beam is reflected from the crystal plane behaving as a specular reflection at the Bragg angle. However, the Bragg reflection physical process has not been integrated into the general‐purpose Monte Carlo simulation toolkit Geant4 for particle physics. In the current study, we developed a new EM physical process class “G4CrystalBraggReflection” and a new EM physical model class “G4DarwinDynamicalModel” for modeling the Bragg reflection physical process within a crystal. We added the Bragg reflection physical process to the EM physics category of Geant4. The preliminary results of photon tracking in a silicon crystal slab have shown the feasibility of simulating the Bragg reflection process in addition to the standard EM processes in the framework of Geant4.

To establish a dose-response relationship between radiation-induced DNA damage and the corresponding absorbed doses in blood irradiated with radionuclides in solution under ex vivo conditions, the absorbed dose coefficient for 1 ml for 1 h internal ex vivo irradiation of peripheral blood (dBlood) must be determined. dBlood is specific for each radionuclide, and it depends on the irradiation geometry. Therefore, the aim of this study is to use the Monte Carlo radiation transport code GATE/Geant4 to calculate the mean absorbed dose rates for ex vivo irradiation of blood with several radionuclides used in Nuclear Medicine. Methods: The Monte Carlo simulation reproduces the irradiation geometry of a blood sample of 7 ml mixed with 1 ml of a water equivalent radioactive solution in an 8 ml vial. The simulation was performed for ten different radionuclides: 18F, 68Ga, 90Y, 99mTc, 123I, 124I, 131I, 177Lu, 223Ra, and 225Ac. Two sets of simulations for each radionuclide were performed with 1x109 histories. The first set was simulated with a mass density of 1.0525 g/cm3 of the blood plus water mixture. The second set of simulations was performed with a mass density of 1 g/cm3 for comparison with previous studies. Results: The values of dBlood for ten radionuclides were calculated. The values range from 10.23 mGy∙ml∙MBq−1 for 99mTc to 15632.02 mGy∙ml∙MBq−1 for 225Ac. The maximum relative change compared to previous studies was 13.0% for 124I. Conclusion: This study provides a comprehensive set of absorbed dose coefficients for 1 ml for 1 h internal ex vivo irradiation of peripheral blood in a special vial geometry and radionuclides typically used in Nuclear Medicine. Furthermore, the method proposed by this work can be easily adapted to a variety of internal irradiation conditions and serve as a reference for future studies.

As an important part of radiation therapy quality assurance, dose verification can verify the accuracy of the treatment dose to the patient’s tumor target area before treatment. At present, the dose verification technology has developed to the stage of three-dimensional dose verification. However, the existing clinical dose verification tools cannot meet the demand for three-dimensional dose verification in heavy ion therapy. In order to quickly and accurately realize three-dimensional dose verification of carbon ion therapy plan, a three-dimensional ionization chamber array was designed by using plexiglass PMMA(polymethyl methacrylate) as the ionization chamber wall and water equivalent phantom. And the structural design of the three-dimensional ionization chamber array was thoroughly studied and verified by Geant4 software. Firstly, by simulating the depth dose distribution of carbon ion beam deposited in water and PMMA phantom with different energies, the distal range ratio of the Bragg peak of the carbon ion beam in water and PMMA phantom was calculated, and the water equivalent thickness factor of PMMA phantom was characterized. Its value is 1.151. Then the effects of the spacing between adjacent ionization chambers and the signal leads on the accuracy of the dose measurement in the three-dimensional ionization chamber array were investigated. The signal crosstalk between adjacent ionization chambers mainly originates from the front ionization chamber, and the degree of crosstalk is inversely proportional to the spacing, the degree of crosstalk accounts for 3% of the dose within the ionization chamber at spacing of 1 mm, and the crosstalk effect can be completely eliminated at spacing of 30 mm. And the interference effect of the signal leads on the dose within the rear ionization chamber is about 1%. Finally, the dose distribution of 100 MeV/u and 200 MeV/u carbon ion beams deposited in the three-dimensional ionization chamber array was simulated, and the distal range of the Bragg peak was obtained in which the carbon ion beam was deposited. It has good agreement compared to the distal range of the Bragg peak in the PMMA phantom, and the deviation is 0.5 mm. The research show that the three-dimensional ionization chamber array can realize the three-dimensional dose verification of heavy ion therapy at the same time, and provides a reference for the development of three-dimensional ionization chamber array. The quality assurance level of carbon ion therapy should be further improved.

Abstract Background The purpose of this work was to obtain the dosimetric parameters of the new GZP3 60Co high-dose-rate afterloading system launched by the Nuclear Power Institute of China, which is comprised of two different 60Co sources. Methods The Monte Carlo software Geant4 and EGSnrc were employed to derive accurate calculations of the dosimetric parameters of the new GZP3 60Co brachytherapy source in the range of 0–10 cm, following the formalism proposed by American Association of Physicists in Medicine reports TG43 and TG43U1. Results of the two Monte Carlo codes were compared to verify the accuracy of the data. The source was located in the center of a 30-cm-radius theoretical sphere water phantom. Results For channels 1 and 2 of the new GZP3 60Co afterloading system, the results of the dose-rate constant (Λ) were 1.115 cGy h−1 U−1 and 1.112 cGy h−1 U−1, and for channel 3 they were 1.116 cGy h−1 U−1 and 1.113 cGy h−1 U−1 according to the Geant4 and EGSnrc, respectively. The radial dose function in the range of 0.25–10.0 cm in a longitudinal direction was calculated, and the fitting formulas for the function were obtained. The polynomial function for the radial dose function and the anisotropy function (1D and 2D) with a $$\uptheta$$ θ of 0°–175° and an r of 0.5–10.0 cm were obtained. The curves of the radial function and the anisotropy function fitted well compared with the two Monte Carlo software. Conclusion These dosimetric data sets can be used as input data for TPS calculations and quality control for the new GZP3 60Co afterloading system.

The mechanics underlying photon and electron interactions was validated using our developed Brachytherapy computer code for high Dose Rate (HDR). By comparing the photon cross-section utilizing multiple physics libraries in the developed code, the results were benchmarked against experimental and theoretical findings. Klein-Nishina and experimental cross-section results were in good agreement with the Livermore library results. For two therapeutically relevant materials, the first scattered electron range was measured within 1 mm and 2 mm, which has significant implications for the interpretation of the kernel dose spikes observed in previous research.

The absorbed fraction and the S factor represent fundamental quantities in MIRD-based dosimetry of radiopharmaceutical therapy (RPT). Although Monte Carlo (MC) simulations represent the gold standard in RPT dosimetry, dose point kernels (DPK) obtained from analytic range–energy relations offer a more practical alternative for charged-particle dosimetry (β- or α-emitters). In this work, we perform DPK- and MC-based calculations of the self-absorbed fractions and S factors for monoenergetic electrons uniformly distributed in intermediate-size target volumes (~mm to cm) relevant to micrometastasis and disseminated disease. Specifically, the aim of the present work is as follows: (i) the development of an analytic range–energy relation, effective over a broad energy range (100 keV–20 MeV) covering most applications of radiotherapeutic interest; (ii) the application of the new formula to DPK-based calculations of the absorbed fraction and S factor and comparison against MC simulations (both published and present work data) as well as the MIRDcell V2.0.16 software, which uses a similar analytic methodology; and (iii) the study of the influence of simulation parameters (step-size, tracking/production cut-off energies, and ionization model) in Geant4-based calculations of S factors. It is shown that the present DPK-based calculations are in excellent agreement (within 1.5%) with the MIRDcell software, while also being in fair agreement with published MC data as well as with the new Geant4 simulations, with average differences of ~20% for the (sub) mm-sized volumes and ~10% for the cm-sized volumes. The effect of the choice of Geant4 simulation parameters was found to be negligible for the examined target volumes (~mm), except for the use of the Penelope ionization model, which may exhibit noticeable discrepancies (up to ~20%) against the Standard and Livermore models. The present work provides quantitative information that may be useful to both the MC- and DPK-based beta dosimetry of micrometastasis and disseminated disease, which represents an important field of application of RPT.

A machine learning (ML) algorithm (deep neural network) is presented to suppress background in muography applications mainly targeting volcanoes. Additionally it could be applied for large scale geological structures, such as ophiolites. The detector system investigated in this article is designed to suppress the low energy background by applying up to 5 lead absorber layers arranged among 8 detectors. This complicated system was simulated with a Monte-Carlo based particle simulation to provide training sample for the ML algorithm. It is shown that the developed deep neural network is capable of suppressing the low energy background considerably better than the classical tracking algorithm, therefore this additional suppression with ML yields in a significant improvement. The target areas of volcanoes lie beneath approximately a kilometer of rock that only a fraction of a percent of muons have enough energy to penetrate. The ML algorithm takes advantage of the directional changes in the absorbers, as well as the correlation between the muons energy and the deposited energy in the detectors. Identifying very high energy muons is also a challenge: the classical algorithm discards considerable fraction of 1 TeV muons which create multiple hits due to bremsstrahlung, while the ML algorithm easily adapts to accept such patterns.

Muography requires a detailed understanding of the absorption of muons in the material situated between the muon source and the detector. A large-statistics (>3 billion event) Geant4 simulation was run to simulate the absorption of muons in different thicknesses of concrete layers and to determine the effect of the material on the energies of muons that were not absorbed. The Geant4 simulation included a simple detector placed directly behind the absorbing material. A Geant4 simulation was also run for the same detector for alpha sources with no absorbing material and the results of this simulation were compared to the signals from the physical detector built in the laboratory and measured using standard alpha sources. The large-statistics simulations using muons of different energies were compared to the predictions of muon absorption from existing literature. The results of the simulations were in good agreement with both the measured signals from the laboratory as well as the predictions from the literature and the general method is found to be well-suited for studies used for muography involving material layers of uniform thickness. [ABSTRACT FROM AUTHOR]

Internal radiation exposure using radiopharmaceuticals, as in nuclear medicine procedures, necessitates the estimation of the S-value to determine and improve the estimates of absorbed doses in at-risk organs and tissues. The S value is defined as the absorbed dose in the target organ per unit of nuclear transformation in the source organ. It is calculated using the specific absorbed fraction, which is an important quantity that connects the deposited energy in the target and emitting source organs. In this study, we applied DoseCalcs, a new Geant4-based tool, to estimate the S values of 18 F using nuclear data from ICRP Publication 107. Geometrical data from ICRP Publications 110 and 143 were used to select four models representing male and female phantoms for adults and 15 years old to study the variability in the S-values arising from variations in anatomy and initial energy validations, because we used the β mean energy instead of the full beta spectrum. The 18 F-released photons and β from 26 source organs were tracked using the Geant4 Livermore package. Accordingly, the S-values were calculated for 141 target organs. The results for the adult male and female phantoms were compared with the OpenDose reference data. These results agreed well with OpenDose, the average ratio for self-absorption S-values was 1.015, and the average ratios for the cross-irradiation were 1.2 and 1.22 for the AM and AF, respectively. This indicates the accuracy of DoseCalcs for subsequent use in estimating 18 F S-values using voxelized geometries. [ABSTRACT FROM AUTHOR]

Positron emission particle tracking (PEPT) has offered important insights into the internal dynamics of multiphase flows. High precision and frequency measurements of the location of the tracer particle are required to resolve individual eddies at the millimetre scale or smaller. To explore the potential of PEPT to perform these measurements, a model was developed of the Siemens ECAT "EXACT3D" HR++ positron emission tomography (PET) scanner at the PEPT Cape Town facility in South Africa with the software Geant4 Application for Tomographic Emission (GATE) and was used to generate Lagrangian tracks from simulations of moving tracer particles. The model was validated with measurements from both experiment and simulation and was extended to two virtual scenarios inspired by turbulent flows. The location data from the simulation accurately captured linear portions of an oscillating path up to high speeds of 25 m s − 1 ; however, tracking tended to undercut the turning points due to the high tracer acceleration. For a particle moving on a spiral path of decreasing radius, the location data tracked the path above a radius of 2.0 mm with an uncertainty equivalent to the radius of the tracer particle, 300 μ m. Improvements to the measurement are required to track sub-millimetre flow structures, such as the application of PET scanners with higher spatial resolution and upgrades to the sampling processes used in location algorithms. [ABSTRACT FROM AUTHOR]

The Monte Carlo method is compared with deterministic methods based on solving the transport equation and the molecular dynamics method. The capabilities of commonly used general-purpose programs (SRIM, PENELOPE, MCNP, FLUKA, and GEANT4) for Monte Carlo simulation of the processes of particle passage through matter are analyzed. Possible ways to develop the Monte Carlo method are discussed. [ABSTRACT FROM AUTHOR]

Gamma‐Ray Glows (GRGs) are high energy radiation originating from thunderclouds, in the MeV energy regime, with typical duration of seconds to minutes, and sources extended over several to tens of square kilometers. GRGs have been observed from detectors placed on ground, inside aircraft and on balloons. In this paper, we present a general purpose Monte‐Carlo model of GRG production and propagation. This model is first compared to a model from Zhou et al. (2016, https://doi.org/10.1016/j.astropartphys.2016.08.004) relying on another Monte‐Carlo framework, and small differences are observed. We then have built an extensive simulation library, made available to the community. This library is used to reproduce five previous gamma‐ray glow observations, from five airborne campaigns: balloons from Eack et al. (1996b, https://doi.org/10.1029/96gl02570), Eack et al. (2000, https://doi.org/10.1029/1999gl010849); and aircrafts from ADELE (Kelley et al., 2015, https://doi.org/10.1038/ncomms8845), ILDAS (Kochkin et al., 2017, https://doi.org/10.1002/2017jd027405) and ALOFT (Østgaard et al., 2019, https://doi.org/10.1029/2019jd030312). Our simulation results confirm that fluxes of cosmic‐ray secondary particles present in the background at a given altitude can be enhanced by several percent (MOS process), and up to several orders of magnitude (RREA process) due to the effect of thunderstorms' electric fields, and explain the five observations. While some GRG could be explained purely by the MOS process, E‐fields significantly larger than Eth are required to explain the strongest GRGs observed. Some of the observations also came with in‐situ electric field measurements, that were always lower than Eth, but may not have been obtained from regions where the glows are produced. This study supports the claim that kilometer‐scale E‐fields magnitudes of at least the level of Eth must be present inside some thunderstorms. Plain Language Summary: Gamma‐Ray Glows (GRGs) are high‐energy radiation that originates from thunderclouds. These radiations fall within the MeV energy range and last for seconds to minutes. The sources of GRGs are typically extended over a few to tens of square kilometers. In this study, we developed a general‐purpose model to understand the production of GRGs, including the cosmic ray fluxes and enhancement by thunderstorm's electric field, propagation, and instrumental response. Using this model, we were able to reproduce and constrain five previously reported airborne GRG observations, two from balloons, and three from aircraft. The results of our study showed that all of the observations could be explained by one of the two expected regimes: one involving purely particle acceleration (MOS: Modification of Spectrum) and the other involving particle multiplication (RREA: Relativistic Runaway Electron Avalanche). Our simulations suggest that the required large‐scale thunderstorm electric fields, which are compatible with our results, are generally larger than what was previously measured. Key Points: A general‐purpose Monte‐Carlo model of gamma‐ray glow production is presentedPlausible Gamma‐ray Glow production conditions are provided for five previous airborne observationsSome cases could be explained by the Modification of Spectrum mechanism only while other require electric fields close to Relativistic Runaway Electron Avalanche process threshold, or above [ABSTRACT FROM AUTHOR]

Scintillation material presents a variety of applications used in radiation environments such as dosimetry, spectrometry, and radiography facility. Neutron radiography is a non-destructive testing (NDT) method that uses a proper scintillator such as LiI/ZnS for neutron detection. This paper investigated the effect of neutron-induced point defects on the optical properties of this scintillator used in TRR's neutron radiography system. The combination of Monte Carlo and atomistic modeling methods was utilized in this regard. The results showed that the induced point defects lead to a more than 10 and 22% reduction in the refractive index and reflectivity of the LiI scintillator at optical wavelength respectively. Moreover, the refractive index of the ZnS scintillator decreases more than 6.4 % by Zn interstitial, Zn vacancy, and S vacancy and increases 8.9 % by S interstitial at optical wavelength. [ABSTRACT FROM AUTHOR]

Thick target neutron yield produced from 80.5 MeV/u 12C ions stopping in the thick Be, C, W, and Pb targets were measured at 0°, 37°, 60° using liquid scintillation detector and the time of flight method. The experimental data were compared with those calculations using the Liege IntraNuclear-Cascade (INCL) implemented in Geant4 and the JAERI Quantum Molecular Dynamics 2.0 (JQMD-2.0) model followed by the Generalized Evaporation Model (GEM) implemented in PHITS, and default model implemented in FLUKA. The results of the three simulation codes with different physics models are similar for beryllium and carbon targets and in good agreement with the experimental data. For tungsten and lead targets, the calculation results from PHITS and FLUKA successfully reproduced the neutron spectra. While the results from GEANT4 overestimate the experimental data above 50 MeV at 0° and significantly underestimated experimental data in the 15–60 MeV energy range at 0°, 37° and 60°. In general, the simulation results of PHITS with the JQMD-2.0 physical model are in good agreement with the experimental data for all targets. [ABSTRACT FROM AUTHOR]

Objective. We present a method for personalized organ dose estimates obtained before the computed tomography (CT) exam, via 3D optical body scanning and Monte Carlo (MC) simulations. Approach. A voxelized phantom is derived by adapting a reference phantom to the body size and shape measured with a portable 3D optical scanner, which returns the 3D silhouette of the patient. This was used as an external rigid envelope for incorporating a tailored version of the internal body anatomy derived from a phantom dataset (National Cancer Institute, NIH, USA) matched for gender, age, weight, and height. The proof-of-principle was conducted on adult head phantoms. The Geant4 MC code provided estimates of the organ doses from 3D absorbed dose maps in the voxelized body phantom. Main results. We applied this approach for head CT scanning using an anthropomorphic voxelized head phantom derived from 3D optical scans of manikins. We compared the estimates of head organ doses with those provided by the NCICT 3.0 software (NCI, NIH, USA). Head organ doses differed up to 38% using the proposed personalized estimate and MC code, with respect to corresponding estimates calculated for the standard (non-personalized) reference head phantom. Preliminary application of the MC code to chest CT scans is shown. Real-time pre-exam personalized CT dosimetry is envisaged with adoption of a Graphics Processing Unit-based fast MC code. Significance. The developed procedure for personalized organ dose estimates before the CT exam, introduces a new approach for realistic description of size and shape of patients via voxelized phantoms specific for each patient. [ABSTRACT FROM AUTHOR]

Polymers are widely used materials that have many medical and industrial applications. Some polymers have even been introduced as radiation-shielding materials; therefore, many studies are focusing on new polymers and their interactions with photons and neutrons. Research has recently focused on the theoretical estimation of the shielding effectiveness of Polyimide doped with different composites. It is well known that theoretical studies on the shielding properties of different materials through modeling and simulation have many benefits, as they help scientists to choose the right shielding material for a specific application, and they are also much more cost-effective and take much less time compared to experimental studies. In this study, Polyimide (C35H28N2O7) was investigated. It is a high-performance polymer, well known for its outstanding chemical and thermal stability, as well as for its high mechanical resistance. Because of its exceptional properties, it is used in high-end applications. The performance of Polyimide and Polyimide doped with different weight fractions of composites (5, 10, 15, 20 and 25 wt.%) as a shielding material against photons and neutrons were investigated using a Monte Carlo-based simulation toolkit Geant4 within a wide range of energies of both photons and neutrons from 10 to 2000 KeVs. Polyimide can be considered a good neutron shielding material, and its photon shielding abilities could be further enhanced when adding different high atomic number composites to it. The results showed that Au and Ag gave the best results in terms of the photon shielding properties, while ZnO and TiO2 had the least negative effect on the neutron shielding properties. The results also indicate that Geant4 is a very reliable tool when it comes to evaluating the shielding properties against photons and neutrons of any material. [ABSTRACT FROM AUTHOR]

Simple Summary: This work describes the development of a fast and accurate machine learning (ML) 3D U-Net dose engine, trained with Monte Carlo (MC) radiation transport simulations, to calculate the dose in rat patients treated in Microbeam Radiation Therapy (MRT) preclinical studies at the Imaging and Medical Beamline at the Australian Synchrotron. Digital phantoms are created based on CT scans of sixteen rats and are augmented to obtain enough anatomical data. Augmented variations of the digital phantoms are then used to simulate with Geant4 the energy depositions of an MRT beam inside the phantoms with 15% (high-noise) and 2% (low-noise) statistical uncertainty. The high-noise MC simulations are used for ML model training and validation, while the low-noise ones for testing. The results show that the ML dose engine provides a satisfactory dose description in the tumor target and generates the dose maps in less than one second. Microbeam radiation therapy (MRT) utilizes coplanar synchrotron radiation beamlets and is a proposed treatment approach for several tumor diagnoses that currently have poor clinical treatment outcomes, such as gliosarcomas. Monte Carlo (MC) simulations are one of the most used methods at the Imaging and Medical Beamline, Australian Synchrotron to calculate the dose in MRT preclinical studies. The steep dose gradients associated with the 50 μ m-wide coplanar beamlets present a significant challenge for precise MC simulation of the dose deposition of an MRT irradiation treatment field in a short time frame. The long computation times inhibit the ability to perform dose optimization in treatment planning or apply online image-adaptive radiotherapy techniques to MRT. Much research has been conducted on fast dose estimation methods for clinically available treatments. However, such methods, including GPU Monte Carlo implementations and machine learning (ML) models, are unavailable for novel and emerging cancer radiotherapy options such as MRT. In this work, the successful application of a fast and accurate ML dose prediction model for a preclinical MRT rodent study is presented for the first time. The ML model predicts the peak doses in the path of the microbeams and the valley doses between them, delivered to the tumor target in rat patients. A CT imaging dataset is used to generate digital phantoms for each patient. Augmented variations of the digital phantoms are used to simulate with Geant4 the energy depositions of an MRT beam inside the phantoms with 15% (high-noise) and 2% (low-noise) statistical uncertainty. The high-noise MC simulation data are used to train the ML model to predict the energy depositions in the digital phantoms. The low-noise MC simulations data are used to test the predictive power of the ML model. The predictions of the ML model show an agreement within 3% with low-noise MC simulations for at least 77.6% of all predicted voxels (at least 95.9% of voxels containing tumor) in the case of the valley dose prediction and for at least 93.9% of all predicted voxels (100.0% of voxels containing tumor) in the case of the peak dose prediction. The successful use of high-noise MC simulations for the training, which are much faster to produce, accelerates the production of the training data of the ML model and encourages transfer of the ML model to different treatment modalities for other future applications in novel radiation cancer therapies. [ABSTRACT FROM AUTHOR]

We address the performance of airborne gamma detection systems equipped with a NaI(Tl) detector to monitor radionuclides in specific areas. In particular, we analyze the use of the fast singular value decomposition (FSVD) algorithm to improve the nuclide recognition ability of the system and effectively trace radioactivity in a complex background environment. We first present a theoretical analysis of the FSVD algorithm and illustrate the nuclide recognition algorithm step by step. The core of the algorithm is singular value decomposition and parameter estimation based on a Gaussian Markov linear regression model. From the estimated values of the parameters, information about radionuclides can be effectively extracted. We assume the presence of a strong background due to a high concentration of 222Rn and its progeny, which is simulated using GEANT4. By adding trace elements of 131I and 137Cs and changing the relative emissivity, the ratio of the total energy peak count of 131I and 137Cs to the background environment interval count of the corresponding 222Rn and its progeny are controlled. Assuming a counting ratio equal to 0.005, the FSVD algorithm is still able to effectively discriminate the presence of a small number of nuclides, reflecting very excellent recognition ability. Finally, based on data from an airborne gamma detection system in a self-control radon chamber, the FSVD algorithm is employed to recognize the trace of 137Cs nuclides in a strong radon background. A DURRIDGE RAD7 radon measuring instrument is used to monitor the radon concentration in the radon chamber. The actual measurement results show that the FSVD algorithm can effectively detect 137Cs nuclides. [ABSTRACT FROM AUTHOR]

In this work, we developed and validated two novel imaging geometries of benchtop multi-pinhole X-ray fluorescence computed tomography (XFCT) systems with Geant4 Toolkit. One of the Monte Carlo (MC) models utilized a fan beam source to illuminate a single slice of the object, a detector and a multi-pinhole collimator to image each slice's X-ray fluorescence (XRF). The other model consisted of a cone-beam X-ray source (designed as a 5 mm wide fan beam to reduce simulation time) to scan the whole object, two detectors and two multi-pinhole collimators to image the emissions. The phantom used in the simulations included four sections, each with three cone-shaped gold nanoparticle (GNP) inserts (5 mm in height, 3 mm in diameter across the top) with center-to-center distances of 4 mm, 4.5 mm and 4.86 mm. The GNPs concentration was 0.1 wt. %, 0.3 wt. %, 0.5 wt. % and 0.7 wt. %, respectively. The diameter of the multi-pinhole collimator was 1 mm. Performance was evaluated for pinhole-detector-distance (PDD) of 5 cm, 3.5 cm and 2.5 cm, and the results for different object layers and for single pinhole and multi-pinhole (9 pinholes) imaging were compared. The data showed that results worsened with decreasing GNPs insert diameters and with decreasing PDD (object-pinhole-distance was fixed). The multi-pinhole configurations performed better than a single pinhole. The detection limit for the first multi-pinhole operation was 0.21 wt. %; the second was 0.24 wt. %. Detection limits for the single pinhole were 0.32 wt. % and 0.35 wt. %, respectively. The first MC model could acquire 2D slice images of the object without rotation and the second MC model could image the 3D object efficiently. These two novel multi-pinhole systems could potentially provide a bioimaging modality for nanomedical applications. [ABSTRACT FROM AUTHOR]

G4NRF (Jordan and Warren, 2007; Vavrek et al., 2018a,b) is a simulation module for modeling nuclear resonance fluorescence (NRF) interactions in the Geant4 framework (Allison et al., 2016). In this work, we validate G4NRF against both absolute and relative measurements of three NRF interactions near 2.2 MeV in 238U and 27Al using the transmission NRF data from the experiments described in Jayson et al. (2018). Agreement between the absolute NRF count rates observed in the data and predicted by extensive Geant4+G4NRF modeling validate the combined Geant4+G4NRF to approximately 15–20% in the 238U NRF transitions and 10% in 27Al, for an average 14% discrepancy across the entire study. The difference between simulation and experiment in relative NRF rates, as expressed as ratios of count rates in various NRF lines, is found at the level of ≲3%, and is statistically identical to zero. Inverting the analysis, approximate values of the absolute level widths and branching ratios for 238U and 27Al are also obtained.

G4NRF (Jordan and Warren, 2007; Vavrek et al., 2018a,b) is a simulation module for modeling nuclear resonance fluorescence (NRF) interactions in the Geant4 framework (Allison et al., 2016). In this work, we validate G4NRF against both absolute and relative measurements of three NRF interactions near 2.2 MeV in 238U and 27Al using the transmission NRF data from the experiments described in Jayson et al. (2018). Agreement between the absolute NRF count rates observed in the data and predicted by extensive Geant4+G4NRF modeling validate the combined Geant4+G4NRF to approximately 15–20% in the 238U NRF transitions and 10% in 27Al, for an average 14% discrepancy across the entire study. The difference between simulation and experiment in relative NRF rates, as expressed as ratios of count rates in various NRF lines, is found at the level of ≲3%, and is statistically identical to zero. Inverting the analysis, approximate values of the absolute level widths and branching ratios for 238U and 27Al are also obtained.

A mathematical model of a 10 MeV industrial electron accelerator was established by using GEANT4 Monte Carlo software package, and the dose distribution of homogeneous products under different densities were obtained by simulation calculation. Combined with the Qt interface design and development platform, the calculated data were designed by C++ programming. The dose distribution and dose uniformity ratio of different product densities and thicknesses were obtained. In addition, Qt was used to interface the product irradiation dose and the conveyor device transmission speed calculation, daily process management, and dose field distribution data drawing, forming the irradiation process interface software. The accuracy of GEANT4 simulation calculation results and process software was verified by using dose distribution tests and industry research results. The experimental results revealed that the calculation results and test results are in good agreement. The irradiation technology interface software, which can be applied to calculate the irradiation effect and transmission speed of products and other main process parameters in real time, is a useful tool for product irradiation technology design.

This study aims to investigate the utility of using 15PbF2–(60x)TeO2–25WO3–xNd2O3 (0.1 ≥ x ≥ 1.5) glasses in the nuclear shielding applications for mixed radiation fields at energies ranging from 15 keV to 15 MeV. The effect of Nd3+ ions on gamma attenuation properties of the present glass system was discussed in detail. The radiation attenuation features were investigated for the present glass system by using Monte Carlo radiation transport simulation via Geant4 toolkit. The simulation results were theoretically approved by using Phy-X approach over the entire considered energy range. The obtained results indicate that the values of Zeff and Neff were both highest in the in the τ/ρ dominated energies due to the atomic number dependence of the cross sections of the τ/ρ absorption processes. Moreover, FNRCS values were 0.1152, 0.1152, 0.1153, and 0.1153 cm−1 for PWTN1, PWTN2, PWTN3, and PWTN4 respectively. Finally, an extensive comparative study is also presented between the studied glass system and standard traditional shielding materials. The study suggests PWTN4 is the best photon shield amongst the studied PWTN-glasses. Resumen: Este estudio tiene como objetivo investigar la utilidad del uso de vidrios 15PbF2–(60x)TeO2–25WO3–xNd2O3 (0,1 ≥ x ≥ 1,5) en las aplicaciones de blindaje nuclear para campos de radiación mixtos a energías que van desde 15 keV hasta 15 MeV. Se discute en detalle el efecto de los iones Nd3+ sobre las propiedades de atenuación gamma de este sistema de vidrio. Se investigan las características de atenuación de radiación para este sistema de vidrio utilizando la simulación de transporte de radiación de Monte Carlo con el conjunto de herramientas Geant4. Los resultados de la simulación se han corroborado teóricamente utilizando la aproximación Phy-X en todo el rango de energías considerado. Los resultados obtenidos indican que los valores de Zeff y Neff fueron los más altos en las energías dominantes en τ/ρ debido a la dependencia con el número atómico de las secciones transversales de los procesos de absorción τ/ρ. Además, los valores de FNRCS fueron 0,1152; 0,1152; 0,1153 y 0,1153 cm−1 para PWTN1, PWTN2, PWTN3 y PWTN4, respectivamente. Por último, también se presenta un extenso estudio comparativo entre el sistema de vidrio analizado y los materiales de blindaje estándar y tradicionales. El estudio muestra que PWTN4 es el mejor escudo de fotones de entre los vidrios PWTN estudiados.

The paper reports the results of simulation of cosmic ray proton transport through Earth’s atmosphere. The main objective of this work is to obtain characteristics of secondary particle fluxes at different altitudes and to convert them to equivalent dose values. The technique for the conversion is based on numerical simulation of interaction between the particles and an anthropomorphic phantom. The paper examines two cases, using a model source of primary proton spectra as input parameters, which correspond to both purely galactic cosmic rays and solar cosmic rays. The computational results are tabulated for the altitude range from 0 km to 11 km above sea level; the upper range value corresponds to the flight altitude of civilian airliners. These results are shown to agree well with the results obtained by other research teams.

Abstract The PADME experiment at the DAΦNE Beam-Test Facility (BTF) of the INFN Laboratory of Frascati is designed to search for invisible decays of dark sector particles produced in electron-positron annihilation events with a positron beam and a thin fixed target, by measuring the missing mass of single-photon final states. The presence of backgrounds originating from beam halo particles can significantly reduce the sensitivity of the experiment. To thoroughly understand the origin of the beam background contribution, a detailed Geant4-based Monte Carlo simulation has been developed, containing a full description of the detector together with the beam line and its optical elements. This simulation allows the full interactions of each particle to be described, both during beam line transport and during detection, a possibility which represents an innovative way to obtain reliable background predictions.

Background: Dynamic positron emission tomography (dPET) is a nuclear medicine imaging technique providing functional images for organs of interest with applications in oncology, cardiology, and drug discovery. This technique requires the acquisition of the time-course arterial plasma activity concentration, called the arterial input function (AIF), which is conventionally acquired via arterial blood sampling. Purpose: The aim of this study was to (A) optimize the geometry for a novel and cost efficient non-invasive detector called NID designed to measure the AIF for dPET scans through Monte Carlo simulations and (B) develop a clinical data analysis chain to successfully separate the arterial component of a simulated AIF signal from the venous component. Methods: The NID was optimized by using an in-house Geant4-based software package. The sensitive volume of the NID consists of a band of 10 cm long and 1 mm in diameter scintillating fibers placed over a wrist phantom. The phantom was simulated as a cylinder, 10 cm long and 6.413 cm in diameter comprised of polyethylene with two holes placed through it to simulate the patient's radial artery and vein. This phantom design was chosen to match the wrist phantom used in our previous proof of concept work. Two geometries were simulated with different arrangements of scintillating fibers. The first design used a single layer of 64 fibers. The second used two layers, an inner layer with 29 fibers and an outer layer with 30 fibers. Four positron emitting radioisotopes were simulated: 18F, 11C, 15O, and 68Ga with 100 million simulated decay events per run. The total and intrinsic efficiencies of both designs were calculated as well as the full width half maximum (FWHM) of the signal. In addition, contribution by the annihilation photons versus positrons to the signal was investigated. The results obtained from the two simulated detector models were compared. A clinical data analysis chain using an expectation maximization maximum likelihood algorithm was tested. This analysis chain will be used to separate arterial counts from the total signal. Results: The second NID design with two layers of scintillating fibers had a higher efficiency for all simulations with a maximum increase of 17% total efficiency for 11C simulation. All simulations had a significant annihilation photon contribution. The signal for 18F and 11C was almost entirely due to photons. The clinical data analysis chain was within 1% of the true value for 434 out of 440 trials. Further experimental studies to validate these simulations will be required. Conclusions: The design of the NID was optimized and its efficiency increased through Monte Carlo simulations. A clinical data analysis chain was successfully developed to separate the arterial component of an AIF signal from the venous component. The simulations show that the NID can be used to accurately measure the AIF non-invasively for dPET scans. [ABSTRACT FROM AUTHOR]

Space missions with humans expose the crews to ionizing radiation, mainly due to the galactic cosmic radiation (GCR). All radiation protection programs in space aim to minimize crews' exposure to radiation. The radiation protection of astronauts can be achieved through the use of shields. The shields could serve as a suit to reduce GCR exposure and, in an emergency, as a radiation shelter to perform necessary interventions outside the space habitat in case of a solar proton event (SPE). A space radiation shielding that is suitable for exploration during space missions requires particular features and a proper knowledge of the radiation type. This study shows the results of numerical simulations performed with the Geant4 toolkit-based code DOSE. Calculations to evaluate the performance of Nomex, an aramidic fiber with high mechanical resistance, in terms of dose reduction to crews, were performed considering the interaction between protons with an energy spectrum ranging from 50 to 1100 MeV and a target slab of 20 g/cm2. This paper shows the properties of secondary products obtained as a result of the interaction between space radiation and a Nomex target and the properties of the secondary particles that come out the shield. The results of this study show that Nomex can be considered a good shield candidate material in terms of dose reductions. We also note that the secondary particles that provide the greatest contribution to the dose are protons, neutrons and, in a very small percentage, α-particles and Li ions. [ABSTRACT FROM AUTHOR]

Most of the traditional studies based on single event effects (SEEs) favor the analysis of electrical mechanisms of semiconductor devices. Professional simulation software in microelectronics requires researchers to have a solid knowledge of microelectronics theory, and the modeling threshold of the software is relatively high, the simulation speed is slow, and accurate simulation of inter‐particle and particle–material interactions is lacking. SEEs are related to linear energy transfer (LET), in this paper, a method is proposed to obtain LET datas to predict SEEs of particles incident on silicon materials by using the Geant4 Monte Carlo toolkit in combination with a dense convolutional network to accurately and rapidly estimate the energy deposition characteristics of the particles. The proposed network structure has a high prediction accuracy with a mean square error （MSE） of only 1.77 × 10−4. Compared with Geant4, which takes 1 min to compute a set of data, the proposed network structure takes only 0.0817 s. The method explores the feasibility of using Geant4 to model semiconductor devices combined with deep learning algorithms, providing a new research perspective for the prediction of microelectronic devices and making it possible to explore the influence of integrated circuits by SEEs. [ABSTRACT FROM AUTHOR]

Purpose: Manufacturing of miniaturized high activity iridium-192 (192Ir) sources have been made a market preference in modern brachytherapy. Smaller dimensions of the sources are flexible for smaller diameter of the applicators, and it is also suitable for interstitial implants. Presently, cobalt-60 (60Co) sources have been commercialized as an alternative to 192Ir sources for high-dose-rate (HDR) brachytherapy, since 60Co source have an advantage of longer half-life comparing with 192Ir source. One of them is the HDR 60Co Flexisource manufactured by Elekta. The purpose of this study was to compare the TG-43 dosimetric parameters of HDR flexi 60Co and HDR microSelectron 192Ir sources. Material and methods: Monte Carlo simulation code of Geant4 (v.11.0) was applied. Following the recommendations of AAPM TG-43 formalism report, Monte Carlo code of HDR flexi 60Co and HDR microSelectron 192Ir was validated by calculating radial dose function, anisotropy function, and dose-rate constants in a water phantom. Finally, results of both radionuclide sources were compared. Results: The calculated dose-rate constants per unit air-kerma strength in water medium were 1.108 cGy h-1U-1 for HDR microSelectron 192Ir, and 1.097 cGy h-1U-1 for HDR flexi 60Co source, with the percentage uncertainty of 1.1% and 0.2%, respectively. The values of radial dose function for distances above 22 cm for HDR flexi 60Co source were higher than that of the other source. The anisotropic values sharply increased to the longitudinal sides of HDR flexi 60Co source, and the rise was comparatively sharper to that of the other source. Conclusions: The primary photons from the lower-energy HDR microSelectron 192Ir source have a limited range and are partially attenuated when considering the results of radial and anisotropic dose distribution functions. This implies that a HDR flexi 60Co radionuclide could be used to treat tumors beyond the source compared with a HDR microSelectron 192Ir source, despite the fact that 192Ir has a lower exit dose than HDR flexi 60Co radionuclide source. [ABSTRACT FROM AUTHOR]

Copyright of Journal Of Sichuan University (Natural Sciences Division) / Sichuan Daxue Xuebao-Ziran Kexueban is the property of Editorial Department of Journal of Sichuan University Natural Science Edition and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The device downscaling of electronic components has given rise to the need to consider specific failures in onboard airplane electronics. Single Event Effects (SEE) are a kind of failures that occur due to radiation in the atmosphere. For the purpose of ensuring onboard electronic reliability, there is a clear need for new tools to predict the SEE rate, at both avionic altitudes and at ground level. In this work, we develop a new tool: RAMSEES (Radiation Atmospheric Model for SEE Simulation), which simulates the atmospheric radiative environment induced by cosmic rays. This multiscale and multi-physics phenomenon is simulated using the Geant4 toolkit, allowing the creation of a database to characterize the radiation environment in the atmosphere as a function of altitude. We show the need to simulate very high-energy particles such as 100 TeV space protons, because they are the main contributor of radiation at avionic altitudes as well as at ground level. Our approach shows a good agreement with the experimental data, the standards, and other models, and it also points out some discrepancies, especially below 18 km of altitude. RAMSEES can be the basis of the estimation of the SEE rate from ground level to the stratosphere, at any given position and time. [ABSTRACT FROM AUTHOR]

Low energy I-125- seeds are considered as a common source in different brachytherapy techniques for treatment of different cancers. In this study, at first, we simulated and validated I-125 (model 6711) seed according to the TG-43U1 recommendation, by GEANT4 Monte Carlo toolkit. Moreover, we simulated new seeds containing cylindrical Ag+Al2O3 markers with different ratio of Ag and Al2O3 in the final composition of the marker and compared the radial dose functions and anisotropy functions of the sources. For validation and evaluation purposes, the radial dose function and anisotropy function were calculated at various distances from the center of the different simulated sources. The source validation results show that GEANT4 Monte Carlo toolkit produces accurate results for dosimetric parameters of the I-125 seed by choosing the appropriate physics list. On the other hand, results show a similarity between calculated dosimetric parameters of the I-125 seed (6711) and other sources, with a percentage difference of about 5%. [ABSTRACT FROM AUTHOR]

X‐ray diffraction from a solid crystal shows the wave nature of photons. It is an important electromagnetic (EM) physics process when X‐ray photons interact with a crystal. Bragg diffraction, often called Bragg reflection, is a special case of the general form of X‐ray diffraction, known as Laue diffraction. When the Bragg's law is met, the incident photon beam is reflected from the crystal plane behaving as a specular reflection at the Bragg angle. However, the Bragg reflection physical process has not been integrated into the general‐purpose Monte Carlo simulation toolkit Geant4 for particle physics. In the current study, we developed a new EM physical process class "G4CrystalBraggReflection" and a new EM physical model class "G4DarwinDynamicalModel" for modeling the Bragg reflection physical process within a crystal. We added the Bragg reflection physical process to the EM physics category of Geant4. The preliminary results of photon tracking in a silicon crystal slab have shown the feasibility of simulating the Bragg reflection process in addition to the standard EM processes in the framework of Geant4. [ABSTRACT FROM AUTHOR]

To establish a dose-response relationship between radiation-induced DNA damage and the corresponding absorbed doses in blood irradiated with radionuclides in solution under ex vivo conditions, the absorbed dose coefficient for 1 ml for 1 h internal ex vivo irradiation of peripheral blood (d Blood) must be determined. d Blood is specific for each radionuclide, and it depends on the irradiation geometry. Therefore, the aim of this study is to use the Monte Carlo radiation transport code GATE/Geant4 to calculate the mean absorbed dose rates for ex vivo irradiation of blood with several radionuclides used in Nuclear Medicine. The Monte Carlo simulation reproduces the irradiation geometry of a blood sample of 7 ml mixed with 1 ml of a water equivalent radioactive solution in an 8 ml vial. The simulation was performed for ten different radionuclides: 18F, 68Ga, 90Y, 99mTc, 123I, 124I, 131I, 177Lu, 223Ra, and 225Ac. Two sets of simulations for each radionuclide were performed with 1x109 histories. The first set was simulated with a mass density of 1.0525 g/cm3 of the blood plus water mixture. The second set of simulations was performed with a mass density of 1 g/cm3 for comparison with previous studies. The values of d Blood for ten radionuclides were calculated. The values range from 10.23 mGy∙ml∙MBq−1 for 99mTc to 15632.02 mGy∙ml∙MBq−1 for 225Ac. The maximum relative change compared to previous studies was 13.0% for 124I. This study provides a comprehensive set of absorbed dose coefficients for 1 ml for 1 h internal ex vivo irradiation of peripheral blood in a special vial geometry and radionuclides typically used in Nuclear Medicine. Furthermore, the method proposed by this work can be easily adapted to a variety of internal irradiation conditions and serve as a reference for future studies. [ABSTRACT FROM AUTHOR]

A pelvic CT scan may be recommended for a pregnant woman in the later stages of pregnancy if there is a possibility that the baby's head may be too large to fit through the pelvis during delivery. This examination assesses the size of the pelvis by measuring different bone diameters and provides information on the pelvis's morphology. Additionally, physicists and doctors frequently worry about ionizing radiation exposure might have a detrimental effect on the foetus. In this study, GATE Monte Carlo toolkit was used to model the SOMATOM EMOTION 16 CT scanner (Siemens Medical Solutions, Erlangen, Germany). The CTDI measurement was used to validate the simulated scanner model for energies 80 kV, 110 kV, and 130 kV. A voxelized phantom in the third trimester was scanned in sequential and helical modes. Organ foetal doses and mean doses were compared at 80 kV, in order to determine the foetal risks associated for each protocol's. The mean foetal doses for sequential and helical mode are 0.74 mGy and 0.90 mGy, respectively. The risks of childhood cancer were 1 in 16,000 and 1 in 17,000 for sequential and helical modes respectively. The risks of hereditary disease were one in 220,000 and other in 270,000 for sequential and helical modes respectively. Although the cumulative dose to the foetus is thought to be less than 100 mGy, the foetal doses were considered acceptable. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Basing our findings on our previous pulsed laser testing results, we have experimentally demonstrated that there is an inflection point of a single event transient (SET) in the silicon-germanium heterojunction bipolar transistors (SiGe HBTs) with a decreasing temperature from +20 °C to −180 °C. Additionally, the changes in the parasitic resistivity of the carrier collection pathway due to incomplete ionization could play a key role. In this paper, we found that the incident-heavy ion's parameters could also have an important impact on the SET inflection point by introducing the ion track structures generated by Geant4 simulation to the TCAD transient simulation. Heavy ion with a low linear energy transfer (LET) will not trigger the ion shunt effect of SiGe HBT and the inflection point will not occur until −200 °C. For high LET ions' incidence, the high-density electron-hole pairs (EHPs) could significantly affect the parasitic resistivity on the pathway and lead to an earlier inflection point. The present results and methods could provide a new reference for the effective evaluation of single-event effects in bipolar transistors and circuits at cryogenic temperatures and provide new evidence of the SiGe technology's potential for applications in extreme cryogenic environments. [ABSTRACT FROM AUTHOR]

Background: The purpose of this work was to obtain the dosimetric parameters of the new GZP3 60Co high-dose-rate afterloading system launched by the Nuclear Power Institute of China, which is comprised of two different 60Co sources. Methods: The Monte Carlo software Geant4 and EGSnrc were employed to derive accurate calculations of the dosimetric parameters of the new GZP3 60Co brachytherapy source in the range of 0–10 cm, following the formalism proposed by American Association of Physicists in Medicine reports TG43 and TG43U1. Results of the two Monte Carlo codes were compared to verify the accuracy of the data. The source was located in the center of a 30-cm-radius theoretical sphere water phantom. Results: For channels 1 and 2 of the new GZP3 60Co afterloading system, the results of the dose-rate constant (Λ) were 1.115 cGy h−1 U−1 and 1.112 cGy h−1 U−1, and for channel 3 they were 1.116 cGy h−1 U−1 and 1.113 cGy h−1 U−1 according to the Geant4 and EGSnrc, respectively. The radial dose function in the range of 0.25–10.0 cm in a longitudinal direction was calculated, and the fitting formulas for the function were obtained. The polynomial function for the radial dose function and the anisotropy function (1D and 2D) with a θ of 0°–175° and an r of 0.5–10.0 cm were obtained. The curves of the radial function and the anisotropy function fitted well compared with the two Monte Carlo software. Conclusion: These dosimetric data sets can be used as input data for TPS calculations and quality control for the new GZP3 60Co afterloading system. [ABSTRACT FROM AUTHOR]

The linear attenuation coefficient (LAC), mean free path (MFP), half-value layer (HVL), and the radiation protection efficiency (RPE) parameters of Lombok pumice powder from 3 different regions (Ijobalit, Setangi beach, and Lingsar) have been analyzed. The radiation parameter analysis was carried out to determine the pumice that potential as a raw material of radiation shielding composite. The Monte Carlo simulation using the GEANT4 toolkit was applied to analyze those parameters using a gamma-ray transmission measurement for the photon energies of 57Co, 133Ba, 54Mn, 137Cs, 60Co, 65Zn, 22Na and 40K. The GEANT4 simulation results were compared to the XCOM theoretical calculation and show that the linear attenuation coefficient parameter has a good agreement with the XCOM results based on the determination coefficient of the correlation graph (R² = 0.998) between those 2 approaches methods. Setangi beach pumice has a smaller LAC parameter than Ijobalit pumice and Lingsar pumice. The MFP and HVL parameter of the Setangi beach pumice indicate the absorption ability of gamma photons is low. In the low gamma energy 0.122 MeV, Ijobalit pumice and Lingsar pumice have more than 50 % RPE and are better used as a raw material of radiation shielding composite. [ABSTRACT FROM AUTHOR]

Background: The purpose of this research was to show how the Bragg peak (BP) characteristics were affected by changing the voxel size in longitudinal and transverse directions in Monte Carlo (MC) simulations by using Geant4 and to calculate BP characteristics accurately by considering the voxel size effect for 68 MeV and 235.81 MeV. Materials and methods: Different interpolation techniques were applied to simulation data to find the closest results to the experimental data. Results: When the x-size of the voxel was increased 2 times at low energy, the maximum dose increase in the entrance and plateau regions were 17.8% and 17%, respectively, while BP curve shifted to the shallower region, resulting in a 0.5 mm reduction in the curable tumor width (W80pd). At high energy, the maximum dose increase at the entrance and plateau regions were 0.4% and 0.6%, respectively, while it was observed that W80pd did not change. When the y-z sizes of the voxel were increased 2 times at low energy, the maximum dose reduction at the entrance and plateau regions was 3.4%, but no change was observed in W80pd. At high energy, when the y-z sizes of the voxel were increased 2.2 times, the maximum dose reduction at the entrance and plateau regions were 8.9% and 9.1%, respectively, while W80pd increased by 0.5 mm. When linear, cubic spline, and Akima interpolations were applied to the simulation data, it was found that the results closest to the experimental data were obtained for Akima interpolations for both energies. Conclusion: it has been shown that the voxel size effect for the longitudinal direction was more effective at low energy than at high energy. However, the voxel size effect for the transverse direction was more effective for high energy. [ABSTRACT FROM AUTHOR]

Mammography machines must meet high requirements to ensure the quality of the generated images. On the other hand, due to the use of ionizing radiation, there is a need to minimize the dose received by patients. To optimize both of these parameters (dose and image quality), the response characteristics of image detectors and, depending on the composition of the breasts, the physical contrast of the examined structures should be considered. This study aimed to determine the optimal voltage values for a given breast thickness during imaging with the use of a selenium image detector. Analysis was carried out using the Monte Carlo simulation method with the GEANT4 code. Our results reveal that the combination of Mo anode together with Mo filtration (the system recommended in analog mammography) was the least favorable combination among those used in digital mammography machines with a selenium detector. Moreover, the use of Rh filtration instead of Mo was advantageous regardless of the thickness of the breast and resulted in a significant improvement in image quality with the same dose absorbed in the breast. The most advantageous solution was found to be an X-ray tube with a W anode. The highest values of the image quality-to-dose ratio were observed for breasts with dimensions ranging from 53 mm to 60 mm in thickness. Lower image quality was observed for breasts with smaller dimensions due to high breast glandularity, resulting in the deterioration of the physical contrast. [ABSTRACT FROM AUTHOR]

El propósito de este estudio es generar la simulación y validación de un haz de cobalto 60 de un equipo de radioterapia en condiciones de referencia, mediante el uso de parámetros de evaluación correspondientes a sistemas de planificación comerciales. Para esto, se utilizaron datos de perfiles de dosis y de porcentaje de dosis en profundidad (PDD) para un tamaño de campo de 10 cm x 10 cm a una distancia fuente superficie (DFS) de 80 cm del maniquí de agua. El programa utilizado para la simulación fue el Geant4, incorporando el haz de radiación, un sistema de colimación y el maniquí. Al comparar los resultados de la simulación con los datos medidos, se obtuvo una diferencia de 3.50 % en la región definida entre el máximo de dosis y el 50 % en la curva de PDD, así como una desviación máxima de 0.96 mm en la zona de acumulación del PDD, además de una desviación de 1.42 mm en la zona de penumbra para el perfil dosis. Para la zona fuera del eje central en el perfil de dosis y en la zona de bajas dosis fueron del 2.41 % y del 2.56 %, respectivamente. Por los resultados obtenidos, se realizó la validación de las condiciones simuladas.